This application is based on and claims priority under 35 U.S.C. xc2xa7 119 with respect to a Japanese Patent Application 2001-197372, filed on Jun. 28, 2001, the entire content of which is incorporated herein by reference.
This invention generally relates to a variable valve timing control apparatus for controlling an opening/closing timing of a valve of an internal combustion engine.
A Japanese Patent Laid-open Application No. 2001-41012 discloses a variable valve timing control apparatus which is provided with a housing, a vane body, an oil pressure control device, and an intermediate position lock pin. The housing is connected to one of a cam shaft of an internal combustion engine and a crank shaft thereof and includes walls radially formed at an interior of the housing. The walls define the interior of the housing into spaces. The vane body is connected to the other one of the cam shaft and the crank shaft and is rotatably disposed in the interior of the housing. The vane body is provided with radially formed vanes for defining each defined space into an advance angle chamber and a retard angle chamber. The oil pressure control device controls an oil pressure to be supplied to the advance angle chamber and the retard angle chamber so as to rotate the vane body relative to the housing. A relative rotational phase between the crank shaft and the cam shaft can be hence varied in response to the rotation of the vane body relative to the housing. The intermediate position lock pin is equipped to the vane body and is projected from the vane body so as to be engaged with an engaging bore defined in the housing when a pressure level in the chambers is lower than a predetermined pressure level. The vane body is then locked by the intermediate position lock pin at an intermediate position between the most advanced angle phase position of the vane body relative to the housing and the most retarded angle phase position thereof relative to the housing.
However, according to the above described variable valve timing control apparatus, the oil for releasing the intermediate position lock pin from the engaging bore is supplied to a pressure receiving surface of the intermediate position lock pin either from the advance angle chamber via a hydraulic passage or from the retard angle chamber via the other hydraulic passage. Accordingly, when restarting the internal combustion engine immediately after being stopped, the intermediate position lock pin may be engaged with the engaging bore so as to maintain the vane body at the intermediate position under the state where the advance angle chamber (or the retard angle chamber) has been filled with the oil. When the vane body is rotated due to a variable torque applied from the cam shaft under the above condition, the volume of the advance angle chamber (or the retard angle chamber) is varied. When the volume of the advance angle chamber (or the retard angle chamber) is decreased, the oil pressure level in the advance angle chamber (or the retard angle chamber) is temporarily increased. On the other hand, when the volume thereof is increased, the oil pressure level therein is returned down to the former oil pressure level. The variation of the oil pressure level acts on the pressure receiving surface of the intermediate position lock pin from the advance angle chamber (or from the retard angle chamber) via the hydraulic passage. Therefore, an operation of the intermediate position lock pin to be engaged with the engaging bore and to be disengaged therefrom is repeatedly performed.
As a result of this, when the variable torque is applied to the vane body before the intermediate position lock pin, which has been disengaged from the engaging bore, is engaged with the engaging bore, the vane body may be rotated relative to the housing. In other words, the phase of the vane body relative to the housing can not be maintained at the intermediate position by the intermediate position lock pin.
Accordingly, the above disclosed variable valve timing control apparatus is still susceptible of certain improvements with respect to assuring the engagement of the intermediate position lock pin with the engaging bore of the housing even when the oil pressure level variation occurs in the advance angle chamber (or the retard angle chamber) due to the variable torque from the cam shaft.
According to a first aspect of the present invention, a variable valve timing control apparatus includes a housing integrally rotated with one of a crank shaft of an internal combustion engine and a cam shaft thereof, a rotor provided in the housing and integrally rotated with the other one of the crank shaft and the cam shaft, a hydraulic chamber defined between the housing and the rotor, a vane assembled in the rotor for dividing the hydraulic chamber into an advance angle chamber and a retard angle chamber, a relative rotation control mechanism for restraining a relative rotation between the rotor and the housing at an intermediate phase position between the most advanced angle phase position and the most retarded angle phase position in response to a fluid supplied to the relative rotation control mechanism and a fluid drained therefrom, and a fluid pressure passage for controlling the fluid supplied to the advance angle chamber, the retard angle chamber, and the relative rotation control mechanism and for controlling the fluid drained therefrom Further, the fluid pressure passage includes a first fluid path for supplying the fluid to the relative rotation control mechanism and for draining the fluid therefrom independently of a second fluid path for supplying the fluid to the advance angle chamber and the retard angle chamber and for draining the fluid therefrom.
Therefore, the fluid supplied to the relative rotation control mechanism and drained therefrom can be controlled regardless of the fluid supplied to the advance angle chamber or the retard angle chamber and drained therefrom.
According to a second aspect of the present invention, the fluid pressure passage further includes a hydraulic pressure control valve for supplying the fluid to the advance angle chamber, the retard angle chamber, and the relative rotation control mechanism and for draining the fluid therefrom. The hydraulic pressure control valve includes a third fluid path for supplying the fluid to the relative rotation control mechanism and for draining the fluid therefrom independently of a fourth fluid path for supplying the fluid to the advance angle chamber and the retard angle chamber and for draining the fluid therefrom.
Therefore, the fluid can be supplied to and/or drained from the relative rotation control mechanism independently of the fluid supplied to and/or drained from the advance angle chamber and the retard angle chamber.